FiiO FT5 90mm Open Planar Magnetic Headphones

The FiiO FT5 is FiiO’s first planar magnetic headphone: an open-back design with a large 90mm driver, a 6µm PAR diaphragm with micron-thin aluminium-silver alloy traces, and 20 N52 magnets per side. Unusually for a planar, it is easy to drive, at 36Ω and 110dB/Vrms, so it works with portable players as well as desktop amps. A magnesium-aluminium alloy frame keeps it light, and it comes with a silver-plated monocrystalline copper cable with swappable 3.5mm and 4.4mm plugs, XLR-4 and 6.35mm adapters, two sets of pads and a leather case. Its awards include TechPowerUp’s Highly Recommended, a VGP 2024 Summer award and a HiVi Best Buy 2024.

Why planar?

In a dynamic driver, a voice coil pushes the diaphragm from one point, which can make different parts of it vibrate unevenly and add distortion in the treble. A planar driver spreads its coil across a large flat diaphragm in a uniform magnetic field, so the whole surface moves together. As FiiO’s engineer explains, that gives lower distortion, more consistent phase and excellent high-frequency performance, closest in principle to electrostatic headphones. FiiO optimised the placement of the FT5’s coils through simulation and testing for consistent phase across all frequencies.

A 6µm diaphragm, balanced for reliability

FiiO didn’t simply chase the thinnest number. A diaphragm that is too thin risks the traces coming away, so after extensive testing the team chose 6µm, about a tenth of a hair, as the ideal balance of sound and reliability. It evaluated PET, PEI and PAR films for dynamics, efficiency, reliability and resolution, and chose PAR, which gives the FT5 its dynamics, detail and a richness of bass not usually found in planars.

Aluminium-silver traces, printed like a chip

In a planar diaphragm almost all the weight is in the metal traces. FiiO chose a light aluminium alloy and added silver to raise conductivity, making the driver easier to power without losing treble detail. The traces are applied with a 28nm-grade process from the semiconductor industry, so their thickness and weight are even across the film, for more consistent diaphragms and more accurate sound.

20 magnets per side, in balance

Each driver has 11 magnets on the inside and 9 on the outside, 20 per channel and 40 in all, placed parallel to the traces so the diaphragm is held evenly between the inner and outer forces for consistent movement and lower distortion. They are N52 neodymium with a flux density of up to 1.5T. With the light diaphragm and efficient traces, that gives a sensitivity of 96dB/mW (110dB/Vrms), so unlike traditional planars the FT5 can be driven by portable players.

Light metal, open back

More magnets mean more weight, so FiiO built the frame from magnesium-aluminium alloy, only 64% as dense as aluminium alloy, for comfortable long sessions. Metal also resists the strong vibrations a 90mm planar produces with bass-heavy music far better than plastic. The back of the driver housing acts as a baffle separating front and rear sound waves, and the grille is designed to control and accelerate the airflow as the driver moves, for treble resolution beyond dynamic headphones and a wide, vast soundstage.

Cable, plugs and pads

The 1.5m cable has 392 strands of high-purity silver-plated monocrystalline copper (23AWG) for a solid, detailed sound. Its swappable plug system (licensed from FABRILOUS) includes 3.5mm and 4.4mm plugs, plus a 3.5mm to 6.35mm adapter and a 4.4mm to XLR-4 balanced adapter, so it fits almost any source. Two pad types change the sound: suede for a balanced, atmospheric and vigorous presentation, and protein leather for a clearer sound, wider soundstage and more detail.

Good to know

• Open-back: sound leaks in and out, so the FT5 is best for listening at home.
• For a lighter, more affordable FiiO planar, see the FT1 Pro; for the flagship, the FT7.
• In the box: FT5, monocrystalline copper cable, 3.5mm and 4.4mm plugs (4.4mm fitted), 6.35mm and XLR-4 adapters, leather storage case, velvet bag, protein leather pads, suede pads (fitted) and user guide.